A N ELECTRON LOCATOR NORMAN D. WEIS and JOHN S. MEEK University of Colorado, Boulder
INPRESENTING the concept of electron arrangement of neutral atoms, it occurred to one author (N. W.) that the data could be graphically shown by use of what we have called an "electron locator," as shown in Figure 1. This device is 30 inches in diameter and is intended for permanent wall mounting when not in use as a classroom demonstration.
The locator has a stationary face which is immovably attached to a plywood backing, spaced so as to allow movement of an inner disc. This disc is shown in Figure 2. Upon rotation of this disc so that the symbol for an element is lined up with the pointer on the face, the perforations on the face permit a black, red, or white background on the inner disc to be ob-
Fi(rur* 1
JOURNAL O F CHEMICAL EDUCATION
servcd and indicate the electronic state of the element. Black dots and a red one indicate the positions of .
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electrons, while a white background indicates an unfilled position. Only one red dot is showm for eilch element and represents the last electrou gained over the preceding element. This enables one to show clearly how the electronic levels are filled in a regular manner through argon, how the transition elements occur as a d level is filled, why the rare earths have similar valences as the inner 4f level is completed, and how the actinides form a similar series with the incomplete 5f orbital. Hund's rule' is also clearly demonstrated. The elements have been color coded so as to indicate the regular elements, the transition elements, the rare earths, and the actinide group. At present, data2as far as mendelevium have been used. The configuration for a number of elements is uncertain and several possibilities are found in the literature. The configuratiolls giving the most uniform progressions were used in making our device. Details of coustruction wvill be sent to interested readers upon request. ~p
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Hum, F., "Linienspektren und periadisches System der Elemente," Julius Springer, Berlin, 1927. LIPSCOMB,Mr. S., "Comprehen~ive Inorganic Chemistry, Vol. I," (edited by R I . C. Sneed, J. L. Mrtynerrl, R. C. Brastcd), 1). Van Kostrand Co., Inc., S e w York, 1953, p. 12. Data for dements 89 through 103: personal oommunieation, G. Seahorg. I
VOLUME 35, NO. 10, NOVEMBER, 1958
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